Ultrasonic Doppler flow measurement devices have enabled a non-intrusive evaluation of blood characteristics. Current correlations of volumetric blood flow rate to Doppler shift frequency are based on very simple acoustic scattering and flow models. The interactions between the ultrasonic beam and whole blood flow is complicated by signal scatter from finite sample volumes, and overlapping of acoustic signals from individual erythrocytes. The signal is also affected by the vessel wall structure which can exhibit large variations in material properties depending on vessel physiology. The proposed research is aimed at developing a numerical model to characterize and quantify the interaction between ultrasonic acoustic waves and blood flow in small and large vessels. The model will accurately correlate the sample volume. Doppler frequency shift and power density with the mean blood velocity and will determine the effect of structural properties of the vessel walls on the ultrasonic echo signature. Laboratory experiments for model validation will be performed at the Pennsylvania State University. The proposed analysis will lead to a better understanding of the acoustic-field velocity interaction in blood vessels. It will be also useful in assessing the validity of widely used simplistic correlations between the Doppler signal and blood velocity. PROPOSED COMMERCIAL APPLICATION: The numerical model will be an important design and calibration tool for ultrasonic blood flowmeters and will be of significant interest to the manufacturers of these devices. The model will also be of interest to medical sonographers who use Doppler echocardiography for interrogation of blood flow in cardiac patients, and for mapping of arterial wall structure which can be altered by vascular diseases such as atherosclerosis. The developed software will be suitable for running on workstations, well within the financial budgets of device manufacturers.